An organic electroluminescence (EL) device using an organic material is a promising solid-state emitting type inexpensive and large full-color display device, and has been extensively developed. In general, an organic EL device includes an emitting layer and a pair of opposing electrodes holding the emitting layer therebetween. Emission is a phenomenon in which when an electric field is applied between the electrodes, electrons are injected from the cathode and holes are injected from the anode, the electrons recombine with the holes in the emitting layer to produce an excited state, and energy is emitted as light when the excited state returns to the ground state.
Conventional organic EL devices have a higher driving voltage than an inorganic light-emitting diode. The luminance or luminous efficiency thereof is also low, and their properties tend to deteriorate significantly. For these reasons, conventional organic EL devices have not been put in a practical use. Although recent organic EL devices have been improved gradually, further improvement in luminous efficiency, prolongation in life time, color reproducibility or the like has been demanded.
The performance of an organic EL device has been improved gradually by improving an emitting material for an organic EL. In particular, improvement in chromatic purity of a blue-emitting organic EL device (shortening of the emission wavelength) is an important technology which leads to improvement in color reproducibility of a display.
As the example of a material used in an emitting layer, Patent Document 1 discloses an emitting material having dibenzofuran. This emitting material is capable of emitting blue light having a short wavelength. However, an organic EL device using this emitting material has a poor luminous efficiency, and hence, further improvement has been desired.
Patent Documents 4 and 5 each disclose a diaminopyrene derivative. Patent Document 2 discloses a combination of an anthracene host and an arylamine. Patent Documents 3 to 5 disclose a combination of an anthracene host with a specific structure and a diaminopyrene dopant. Further, Patent Documents 6 to 8 disclose an anthracene-based host material.
In each material and in each combination, although it can be admitted that emission properties are improved, emission properties are not yet sufficient. Under such circumstances, an emitting material capable of realizing a high luminous efficiency and capable of emitting light at a further shorter wavelength has been demanded.
Patent Document 9 discloses the use of an aromatic amine derivative which has an arylene group at the central thereof and in which a dibenzofuran ring is bonded to a nitrogen atom as the hole-transporting material. Patent Document 10 discloses the use of an aromatic amine derivate in which a dibenzofuran ring, dibenzothiophen ring, a benzofuran ring, a benzothiophen ring or the like is bonded to a nitrogen atom through an arylene group as a hole-transporting material. However, no example is given in which this aromatic amine derivative is used as an emitting material.